This application claims the priority of German Application No. 199 44 453.6 filed Sep. 16, 1999, which is incorporated herein by reference.
This invention relates to a piston ring to be seated in the top circumferential groove of a piston of an internal-combustion engine. The piston ring has a rounded contact face, whose crest line is situated by more than one-half of the axial piston ring height underneath the radial piston ring flank oriented towards the piston crown.
German Offenlegungsschrift (application published without examination) 39 40 301 describes a piston ring of the above-outlined construction. The contact face of the piston ring has an asymmetrical rounded (convex) contour. Piston rings of this type are seated in the top and second piston grooves and are designated as compression rings.
Conventionally, pistons for internal-combustion engines are provided with a piston ring set composed of a first and a second compression ring and an oil control (oil scraper) ring.
In the endeavor to best adapt the individual piston rings to their assigned tasks, a great number of piston ring constructions have been known. Thus, German Patent No. 4,429,649 describes a special rounded contour for a compression piston ring. The piston ring is designed to be particularly wear resistant. Piston rings intended to be seated in the top piston groove have been designed up to now such that they engage the cylinder wall with a high surface pressure.
Measures which are directed to improve the oil scraping effect have been provided only for piston rings seated in the second or third piston groove.
It is an object of the invention to provide a piston ring for the top piston groove which is improved with respect to its oil scraping effect.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the piston ring includes a first radial flank, a second radial flank; and an outer rounded circumferential surface constituting a contact face of the piston ring. The rounded surface has a circumferential crest line situated at a distance from the first radial flank which is more than one half of the axial piston ring height. The piston ring further has facing end surfaces defining a ring gap; and a circumferential groove provided in the outer rounded circumferential surface and extending axially from the second radial flank to the crest. The circumferential groove terminates adjacent each end surface at a distance therefrom.
By virtue of the special configuration of the contact face (running face) of the piston ring, a combination piston ring is provided which functions as a compression ring as well as an oil scraping ring. That region of the contact face of the piston ring which is closer to the piston crown functions as the compressing part whereas the ring region more remote from the piston crown operates as an oil scraping part.